As is generally well known, conventional radial rotary shaft lip seals are employed with a rotating shaft extending from a housing (enclosure) containing oil (or other fluid media), such as a pump or a motor. These seals operate to prohibit leakage of the fluid media to the atmosphere or lower pressure region, along the surface of the rotary shaft. Contact between the lip seal and the surface of the shaft is subject to various leakage contributors during use of the seal.
Generally, these seals are not pressure balanced and have a lower limited combined pressure and surface-speed application range when higher pressures and higher surface speeds are present due to increased heat generation and wear of the dynamic “Lip Seal Contact Area” where it interferes with the rotating shaft leading to premature seal failure and consequent equipment failure as fluid would leak out of the housing (enclosure).
Often seal face leakage rates will depend on pump/motor operating conditions. If operating vibration levels are high, the shaft suffers from excessive radial or axial movement or is misaligned excessively, leakage rates tend to be higher. Typically, seals leak more during dynamic operation than in a static condition under fluid pressure. During shaft rotation, a fluid film develops between the seal faces to separate them with a larger gap, which causes higher leakage. The dynamic operation may establish a non-flat face pattern which may leak more than when the seal is running. Wear of the seal contact portion, surface finish or roughness of the shaft, abrasives in the fluid are another contributors to leakage.
Accordingly, in one approach, efforts have been made to balance the lip seal by way of pressure or mechanical elements so as to compensate for wear and maintain positive contact thereof with the surface of the rotary shaft.
In another approach, U.S. Pat. No. 4,889,349 issued to Muller on Dec. 26, 1989 discloses a sealing arrangement wherein the lip seal is balanced by an O-ring with further use of the fluid pressure to force the O-ring into the contact with the lip seal.
However, it has been determined that further improvements are necessary to compensate for wear of the lip seal so as to minimize the fluid media leakage, particularly in applications associated with higher differential fluid media pressure and higher rotational speeds of the shaft.